Cardiac pacer

ABSTRACT

The forces which are imparted by a cardiac pacer to adjacent tissues are below the threshold of troublesome difficulty when the body is subjected to acceleration or deceleration. Such below-threshold forces are attributed to controlling the weight of the cardiac pacer to be less than 100 grams, and to controlling the specific gravity to be less than 1.7. Such low density and low weight are attainable by reason of the use of a miniaturized oscillator featuring complementary metal oxide semiconductors consuming such a small power that more than 5 years of life are attainable from the thionyl chloride-lithium type of battery having a prolonged stable voltage of at least 3.3 volts. The cardiac pacer is thin enough to avoid troublesome bulging of the skin adjacent the implanting location.

llnited States Patent Kolenik Dec. 16, 1975 [54] CARDHW PACER OTHERPUBLICATIONS [75] Inventor: Steve Kolemk Leechburg Greatbatch et al.,IEEE Transactions on Biomedical [73] Assignee: ARCO Medical ProductsCompany, g n ering, V. ENE-18, N0. 5, Sept. 1971, pp.

Leechburg, Pa. 317423.

[22] Filed May 1975 Primary Examiner-William E. Kamm [21] Appl. No.1574,199 Attorney, Agent, or Firm-John R. Ewbank Related US. ApplicationData [63] Continuation-impart of Ser, No. 477,571, June 10, [57]ABSTRACT 1974, abandoned- The forces which are imparted by a cardiacpacer to adjacent tissues are below the threshold of troublel CL 123/419128/419 128/419 some difficulty when the body is subjected to acceler-136/156 ation or deceleration. Such below-threshold forces are [51]I111. (11. attributed to ontrolling the weight of the ardiac 1 1 FieldOf Search-M 128/419 P, 419 PG, 419 PS, pacer to be less than 100 grams,and to controlling the 128/419 421, 422, 423; 136/86 F, 153; specificgravity to be less than 1.7. Such low density 307/304, 313 and lowweight are attainable by reason of the use of a miniaturized oscillatorfeaturing complementary 1 References Cited metal oxide semiconductorsconsuming such a small UNITED STATES PATENTS power that more than 5years of life are attainable 3,474,353 10/1969 Keller, Jr. 128/419 PGfrom the thionyl Chloridelithium yp Of battery 3 20 220 11/1971 MurphyJR I 12 419 p5 ing a prolonged stable voltage of at least 3.3 volts. The3,649,367 3/1972 Purdy 128/419 P cardiac pacer is thin enoughto avoidtroublesome 3,743,923 7/1973 Steudel 307/304 bulging of the skinadjacent the implanting location. 3,822,707 7/1974 Adducci et a1.128/419 PS 3,835,864 R8801 128/419 PG 3 Claims, 5 Drawing Figures US.Patent Dec. 16, 1975 CARDIAC PACER RELATED APPLICATION This is acontinuation-in-part of Ser. No. 477,571, filed June 10, 1974, and nowabandoned.

FIELD OF INVENTION This invention relates to cardiac pacers suitable forimplantation and particularly to overcoming the adverse side effectsheretofore observed in connection with prior art use of some types ofimplantable cardiac pacers.

HISTORY OF PRIOR ART In a hospital in which a patient under intensivecare can receive electrical pulse signals from an external oscillator,the size and complexity of the signal generating apparatus is of onlyminor importance. Any implantable cardiac pacer, however, must besufficiently miniaturized to permit surgical placement in a cavitywithin the body. As used herein, the lead (or conduit or catheter) isdeemed a supplement to the pacer, although others have designated thecombination of the lead and unit generating pulses as a pacer. Anelectrical conduit, sometimes called a catheter, transmits theelectrical signals from the implanted cardiac pacer to an appropriatesignal-receiving zone of the heart. A significant portion of implantedcardiac pacers have employed batteries comprising mercury. Such mercurybatteries generate a gas which must be vented from the battery chamber.Such venting has complicated the problem of preventing the eventualpenetration of body fluids into undesired portions of the cardiac pacer.The durability of a mercury battery has permitted usage for more than ayear but generally less than 4 years. A variety of other types ofbatteries, including batteries comprising a lithium anode, have beenproposed for use with cardiac pacers but the numerous problems relatedto the long-term reliability has left most of the needs unanswered.

When a heart pacer, which generally weighs from about 200 to 500 grams,is implanted in the body, the bulge in the skin at the zone ofimplantation is troublesome to the patient. The tissue adjacent thecavity in which the heart pacer is implanted is subjected to severeforces under certain jolting conditions or other rapid acceleration ordeceleration conditions in which the inertia of the heart pacer impartsforces to such tissue adjacent the implantation cavity. It is well knownthat bruising, sense of pain, and/or other biological phenomena areinfluenced by threshold phenomena. As long as the forces are below thethreshold, no biological response is apparent but above the threshold,increasing force involves increasing biological response.

Initially, only older patients were treated with implanted heart pacers.As their usefulness became better known, it was recognized that certaintypes of cardiac problems in children are best treated with heartpacers. Some children needing implanted heart pacers were too small topermit implantation of the previously available heart pacers, and thecontinuing reports of deaths of such children has provided along-standing demand for miniaturized pacers for cardiac patients.

SUMMARY OF THE PRESENT INVENTION In accordance with the presentinvention, a cardiac pacer is maintained at a weight less than 100 gramsand at a specific gravity less than 1.7, whereby the inertia forcesattributable to acceleration and deceleration are below the threshold ofsignificant trouble to the tissue adjacent the cavity of implantation,whereby the patient may wear the implanted cardiac pacer with greatercomfort than prior art cardiac pacers. Such small size and low specificgravity for the heart pacer are attributable in part to the utilizationof oscillator means featuring the use of complementary metal oxidesemiconductor devices which not merely occupy a small volume, but moreparticularly utilize significantly less power per day, whereby thebattery life is significantly prolonged. In accordance with the presentinvention, the sub-threshold weight, sub-threshold density, andacceptable battery life are achieved in part by the combination of saidcomplementary metal oxide semiconductor devices and a battery featuringthe combination of a lithium anode and a thionyl chloride electrolyte.No gas is evolved by the generation of current from the thionyl chloridetype battery. One of the most significant and unique characteristics ofsuch thionyl chloride battery is the attainment of a voltage of about3.3 volts or more over a battery life of more than 5 years. Theinvention features a metal casing effective in shielding the electriccomponents from electromag netic interference. At least two lithiumthionyl chloride type batteries may desirably be maintained in parallelwith circuit means protecting the pacer from interferences attributableto failure of one battery while assuring redundant reliability ofparallel batteries.

The smallness of the cardiac pacer permits its implantation in an infanta few weeks old, thus fulfilling a long-standing demand for a pediatricpacer for cardiac patients.

The nature of the present invention is further clarified by reference todescriptions of appropriate embodiments which merely illustrate and donot restrict the invention.

DESCRIPTION OF DRAWINGS FIG. 1 is a schematic drawing showing a heartpacer implanted in a body so that the electrical conduit can directstimulating pulse to an appropriate zone of a heart.

FIG. 2 is a schematic drawing of a sub-threshold inertia cardiac pacerof the present invention.

FIG. 3 is a perspective view of the heart pacer.

FIG. 4 is a schematic partially sectional end view of FIG. 3.

FIG. 5 is a schematic showing of a heart pacer exerting forces upon thetissue of the walls of the cavity in which it is placed. Differentialacceleration and/or deceleration attributable to differential inertia ofthe heart pacer relative to such adjoining tissue during periods whenrapid shifts of acceleration and/or deceleration occur, impart suchforces upon such tissues.

DESCRIPTION OF INVENTION As shown in FIG. 1, a heart pacer 10 iselectrically and mechanically connected to an electrical conduit 11carrying electrical impulses to a signal reception zone 12 of a heart 13of a mammal 14. The electrical conduit may be directed through a vein 15toward the signal reception zone 12. The heart pacer 10 is implantedwithin a cavity l6. Heretofore, surgeons have employed any of severalcavities such as 17a, l7biand' 17c as alternative cavities for heartpacer implantation. The small size and weight of the heart pacer of thepresent invention is so much less than that of prior heart-.pac'ers thatadditional locations might be suitable for implantation;

As shown in FIG. 5, a heart pacer -10 can be posi-. tioned within acavity 516. The walls 18 of cavity to transmit mechanical forces arisingfrom shifting of heart pacer l0 and may compress and/or stretch tissue519 near cavity walls 18.

In FIG. 5, there is a schematic showing of compression of tissue 51% andthe stretching of tissue 519a as a result of inertial shifting of heartpacer 516 toward wall 180. The specific gravity of heart pacer 51.0 isgreater than the specific gravity of tissue 519 so that when mammal 14is jerked back and forth, the inertia of heart pacer 510 is notidentical to the inertia of the tissue 519, thereby causing differentialinertial forces.

Using the heavy heart pacers of the prior art, differences in weightand/or density amongst the heart pacers appear to be of littleconsequence because all heartventional differential inertial forces,whereby the heart pacer may be worn with significantly greater comfortand with less likelihood of trauma, infection, inflammation, and/orother adverse developments in the tissue adjacent the walls of thecavity in which the heart pacer is implanted. In accordance with thepresent invention, there is greatly decreased likelihood of discomfortfor the person having an implanted heart pacer by reason of the controlof the density and weight of the heart pacer to be so low as to be belowthe threshold of significant discomfort from the differential inertialforces arising from the plausible acceleration-deceleration forces towhich the wearer might be subjected.

As shown in FIG. 2, a heart pacer 210 comprises a casing 230. Suchcasing is made of titanium to assure adequate inertness to thebiological fluids. In a preferred embodiment, a partition 231 dividesthe interior of the casing into a circuitry chamber 232 and a batterychamber 233. A socket 234 is adapted to receive a plug portion ofelectrical conduit 11. The socket 234 is an insert within a moldedorganic polymeric shield 235 which protects a wire 236 extending fromupper por- 4 the battery and positive grounding to the casing 230, as byhaving a casing of the circuitry unit in electrical contact with casing230.

The positive pole of batteries are associated electrically with casing236. Wires 252 and 253 from passthroughs 254 and 255 are energizedrespectively by wire 256 from a standard battery and by wire 257 from asupplemental battery. A negativeterminal 258 of standard battery 260supplies current to wire 256 and thence to pass-through 254, and wire252 and thence to circuitry means, conveniently designated as circuitryunit (1). Similarly, supplemental battery 261 supplies current to wire257, pass-through 255, wire 253 and thence to circuitry unit 256. Thus,power from parallel batteries 260 and 261 in chamber 233 is supplied tocircuitry, unit 256 in chamber 232.

Each of the pass-throughs comprises an insulating member, desirablyconstructed of alumina, sealed to a pin and brazed in an opening inpartition 231, thus closely resembling the structure of pass-through238. Wires 262 and 263 assure *the good electrical'connection betweenthe positiveposts of batteries 260, 261

tion of an electrical pass-through 238 through the roof 239 of circuitrychamber 232. Any electrical signal directed to the electricalpass-through 238 is transmitted to the upper portion 237 and thence towire 236 to socket 234, all electrical components being'anchored withinplastic shield 235. The electrical pass-through metic sealing betweenthe circuitry chamber 232 and the zone of plastic shield 235.

Within circuitry chamber 232'is a circuitry unit 250 having an outputwire 251 directed to said pass-through" pin 2410. The circuitry unit 250is energized by the combination of wire means from the negative pole ofwith casing 230.

"It should be noted that in a preferred embodiment, the batteries 266and 261 are connected electrically in parallel within hermeticallysealed battery chamber 233 andthat the power of two batteries istransmitted through pass-throughs 254 and 255 independently to thecircuitry unit 250. Various materials, such as body fluids from cavity16 and/or fluids within a battery might adversely affect operation ofthe circuitry unit 250 if any leakage occurred. However, because in suchpreferred embodiment circuitry chamber 232 is hermetically sealed, bothfrom cavity 16 and from battery chamber 233, the circuitry unit 250 hasappropriate protection against any leakage which might occur. Ofparticular importance, in all embodiments, casing 36 is hermeticallysealed from cavity 16 so that the heart pacer is protected from theeffects of liquids and/or gases'in cavity 16.

Particular attention is directed to the fact that battery 260 features alithium anode 270 and an electrolyte consisting predominantly of thionylchloride 271. Because battery 26tl features the combination of lithiumanode 270 and thionyl chloride electrolyte 271, its voltage can be ashigh as 3.64 volts and is assuredly at least 3.3 volts during a lifetimeof more than 5 years. Of particular importance,.the voltageof suchlithium-thionyl chloride type battery remains substantially constantduring substantially all of the life. expectancy of the battery anddiminishes significantly only during a few months of theterminal periodof use of the battery. The decreasin g voltage and'thus alteration ofthe pulse rate, provides the clue indicative of theappropriateness of achange of batteries. It is especially important that there be aprocedure for detection of battery depletion. The combination of lithiumanode and thionyl chloride achieves this highly significant desiderata.

In a constant rate heart pacer, the signal pulses to the heart representonly about A; of l per cent of the time during which the heart pacer isimplanted. Accordingly, the battery life for a heart pacer issignificantly influenced by the current drain during the 799/800sfraction of the time when no pulse is sent even though the circuitryunit must be operative. Any demand circuitry sensitive to the normaloperation of the heart delivers impulses to the heart during a timefraction less than the delivery time fraction for a fixed rate heartpacer. Early types of heart pacers were based upon circuitry energizedby a voltage supply of about 6 volts. Significant power was consumed by6 volt circuitry, thereby shortening battery life.

Circuitry unit 250 is characterized by oscillator means employingcomplementary metal oxide semiconductor devices operable at a lowvoltage, so that the two lithium batteries can be connected in parallelinstead of in series. Moreover, such complementary metal oxidesemiconductor devices of the oscillator means permit the circuitry unitto function much of the time at a current drain which is so small thatbattery life can be based to a significant extent upon the dissipationof power at the signal reception zone 12 of the heart. The powerconsumption during the quasi-dormant portion of use is particularlysignificant in connection with demand pacers, in which the combinationof thionyl chloride-lithium batteries and complementary metal oxidesemiconductor devices are particularly advantageous.

The nature of the cardiac pacer of the present invention can beclarified by noting that the pacer consists essentially of thecombination of a metal casing hermetically sealing the interior zones ofthe cardiac pacer from exposure to body fluids in the cavity in whichthe cardiac pacer is implanted, said casing being less than mm thick,and each other orthagonal dimension being less than 60 mm, such smalldimensions permitting implantation without troublesome bulging of theskin adjacent the cardiac pacer, said metal casing shielding electricalcomponents from electromagnetic interference; at least one battery insaid casing, each battery generating no gas, each battery having alithium anode and an electrolyte consisting predominantly of thionylchloride, each battery having prolonged low impedance and constant highvoltage of at least 3.3 volts during an expected life of more than 5years, the voltage diminishing significantly only during the terminalperiod of use of the battery, whereby detection of battery depletion ismanageable; in a preferred embodiment there are wires and pass-throughswithin the casing associating at least two batteries in parallel andprotecting other circuit means from interference attributable to failureof one battery while assuring the redundant reliability of parallelbatteries; employing complementary metal oxide semiconductor circuitmeans for producing pulses adapted to stimulate the heart, said circuitmeans being electrically energized by current supplied by thecombination of wire means from the negative pole of the battery andpositive grounding to the casing of the cardiac pacer, said circuitmeans desirably being within a circuitry chamber within said samllcasing; said complementary metal oxide semiconductors and said circuitrymeans consuming such a small amount of power that the battery life ismore than 5 years; electrical socket means adapted to transmit to anelectrical conduit said electrical pulses suitable for stimulating theheart; and said combination of casing, batteries, wires, pass-throughs,circuit means, and electrical socket means having a weight less than 100grams and a specific gravity less than 1.7, whereby changes inacceleration or deceleration of a body having such implanted cardiacpacer impart only forces which are tolerable to tissue adjacent thecavity in which the cardiac pacer is implanted.

6 Various modifications of the invention are possible without departingfrom the scope of the appended claims.

It is claimed:

1. A cardiac pacer consisting essentially of the combination of:

a metal casing hermetically sealing the interior zones of the cardiacpacer from exposure to body fluids in the cavity in which the cardiacpacer is implanted, said casing being less than 20 mm thick, and eachother orthagonal dimension being less than mm, such small dimensionspermitting implantation without troublesome bulging of the skin adjacentthe cardiac pacer, said metal casing shielding electrical componentsfrom electro-magnetic interference and constituting a groundingelectrode for the cardiac pacer;

a hermetically sealed battery chamber and a hermetically sealedcircuitry chamber within said casing;

a plurality of batteries in said battery chamber, there being anelectrical conductor transmitting battery power from each battery tosaid circuitry chamber, each battery generating no gas, each batteryhaving a lithium anode and an electrolyte consisting predominantly ofthionyl chloride, each battery having prolonged low impedance andconstant high voltage of at least 3.3 volts during an expected life ofmore than 5 years, the voltage diminishing significantly only during theterminal period of use of the battery, whereby detection of batterydepletion is manageable, the positive pole of the batteries beinggrounded to the metal casing;

wires and pass-throughs within the casing associating at least twobatteries in parallel and assuring the redundant reliability of parallelbatteries;

a circuitry unit employing complementary metal oxide semiconductorcircuit means for producing pulses adapted to stimulate the heart, saidcircuit means being electrically energized by current from saidbatteries, the casing of the circuit means being grounded to the casingof the heart pacer, said circuit means being within said circuitrychamber, said circuit means including an output wire, said wires andpass-throughs being electrically connected to said circuit means;

said complementary metal oxide semiconductors and said circuit meansconsuming such a small amount of power that the battery life is morethan 5 years;

electrical socket means adapted to transmit to an electrical conduit theoutput from said circuit means, said electrical conduit being adapted totransmit the output from said circuit means to a signal-receiving zoneof a heart, electrical passthrough means connecting said output wire tosaid socket means; and

said combination of casing, batteries, wires, passthroughs, circuitmeans, and electrical socket means having a weight less than grams and aspecific gravity less than 1.7, whereby changes in acceleration ordeceleration of a body having such implanted cardiac pacer impart onlyforces which are tolerable to tissue adjacent the cavity in which thecardiac pacer is implanted.

2. The cardiac pacer of claim 1 in which the casing consists oftitanium.

3. The cardiac pacer of claim 1 in which the electrical socket means isan insert within a molded organic plastic shield.

1. A CARDIAC PACER CONSISTING ESSENTIALLY OF THE COMBINATION OF: A METALCASING HERMETICALLY SEALING THE INTERIOR ZONES OF THE CARDIAC PACER FROMEXPOSURE TO BODY FLUIDS IN THE CAVITY IN WHICH THE CARDIAC PACER ISIMPLANTED, SAID CASING BEING LESS THAN 20 MM THICK, AND EACH OTHERORTHAGONAL DIMENSION BEING LESS THAN 60 MM, SUCH SMALL DIMENSIONSPERMITTING IMPLANTATION WITHOUT TROUBLESOME BULGING OF THE SKIN ADJACENTTHE CARDIAC PACER, SAID METAL CASINFG SHIELD ING ELECTRICAL COMPONENTSFROM ELECTRO-MAGNETIC INTERFERENCE AND CONSTITUTING A GROUNDINGELECTRODE FOR THE CARDIAC PACER; A HERMETICALLY SEALED BATTERY CHAMBERAND A HERMETICALLY SEALED CIRCUITRY CHAMGER WITHIN SAID CASING; APLURALITY OF BATTERIES IN SAID BATTERY CHAMBER, THERE BEING ANELECTRICAL CONDUCTOR TRANSMITTING BATTERY POWER FROM EACH BATTERY TOSAID CIRCUITRY CHAMBER, EACH BATTERY GENERATING NO GAS, EACH BATTERYHAVING A LITHIUM ANODE AND AN ELECTROLYTE CONSISTING PREDOMINANTLY OFTHIONYL CHLOTRIDE, EACH BATTERY HAVING PROLONGED LOW IMPEDANCE ANDCONSTANT HIGH VOLTAGE OF AT LAST 3.3 VOLTS DURING AN EXPECTED LIFE OFMORE THAN 5 YEARS THE VOLTAGE DIMINISHING SIGNIFICANTLY ONLY DURING THETERMINAL PERIOD OF USE OF THE BATTERY, WHEREBY DETECTION OF BATTERYDEPLETION IS MANAGEBLE, THE POSITIVE POLE OF THE BATTERIES BEINGGROUNDED TO THE METAL CASING; WIRES AND PASS-THROUGHS WITHIN THE CASINGASSOCIATING AT LEAST TWO BATTERIES IN PARRALLEL AND ASSURING THEREDUNDANT RELIABILITY OF PARALLEL BATTERIES; A CIRCUITRY UNIT EMPLOYINGCOMPLEMENTARY METAL OXIDE SEMICONDUCTOR CIRCUIT MEANS FOR PRODUCINGPULSES ADAPTED TO STIMULATE THE HEART, SAID CIRCUIT MEANS BEINGELECTRICALLY ENERGIZED BY CURRENT FROM SAID BATTERIES, THE CASING OF THECIRCUIT MEANS BEING GROUNDED TO THE CASING OF THE HEART PACER, SAIDCIRCUIT MEANS BEING WITH SAID CIRCUITRY CHAMBER, SAID CIRCUIT MEANSINCLUDING AN OUTPUT WIRE, SAID WIRE AND PASS-THROUGH BEING ELECTRICALLYCONNECTED TO SAID CIRCUIT MEANS; SAID COMPLEMENTARY METAL OXIDESEMICONDUCTORS AND SAID CIRCUIT MEANS CONSUMING SUCH A SMALL AMOUNT OFPOWER THAT THE BATTERY LIFE IS MORE THAN 5 YEARS; ELECTRICAL SOCKETMEANS ADAPTED TO TRANSMIT TO AN ELECTRICAL CONDUIT THE OUTPUT FROM SAIDCIRCUIT MEANS SAID ELECTRICAL CONDUIT MEANS BEING ADAPTED TO TRANSMITTHE OUTPUT FROM SAID CIRCUIT MEANS TO A SIGNAL-RECEIVING ZONE OF AHEART, ELECTRIICAL PASS-THROUGH MEANS CONNECTING SAID OUTPUT WIRE TOSAID SOCKET MEANS; AND SAID COMBINATION OF CASING BATTERIES, WIRESMPASS-THROUGHS CIRCUIT MEANS, AND ELECTRICAL SOCKET MEANS HAVING A WEIGHTLESS THAN 100 GRAMS AND A SPECIFIC GRAVITY LESS THAN 1.7 WHEREBY CHANGESIN ACCELERATION OR DECELERATION OF A BODY HAVING SUCH IMPLANTED CARDIACPACER IMPART ONLY FORCES WHICH ARE TOLERABLE TO TISSUE ADJACENT THECAVITY IN WHICH THE CARDIAC PACER IS IMPLANTED.
 2. The cardiac pacer ofclaim 1 in which the casing consists of titanium.
 3. The cardiac pacerof claim 1 in which the electrical socket means is an insert within amolded organic plastic shield.